This invention relates generally to the field of spas and hot tubs, and relates more specifically to safety shutoff devices for this type of equipment. Spas and hot tubs present special problems of electrical safety, since they are necessarily operated in a wet environment, by persons who would be subject to serious electrical shock if they came in contact with live electrical wiring. Providing a simple electrical switch for operation of a spa pump motor, and locating that switch out of reach of anyone in the spa, is not a completely safe acceptable solution to the problem. Air-actuated switches have been developed to address this difficulty. These electrical switches are operated pneumatically, by means of a long tube or control line connecting the switch to a manually operated plunger. Depressing the plunger increases the air pressure in the tube, thereby operating the electrical switch. This permits location of the plunger beside the spa, for convenience of operation. Typically, the switch toggles between "off" and "on" positions each time the plunger is depressed. In this manner the electrical circuitry is effectively isolated from the user's wet environment.
Another difficulty with spas and tubs is that they should not be operated if the water is below a preselected level, to avoid damage to pumps and other equipment. Some form of water level sensor is typically used to take care of this difficulty. Water level sensors can be in the form of electrical contacts connected to the electrical circuitry of the pump, but there is again an inherent risk that exposure of any electrical circuitry to the wet environment of the tub may lead to electrical shock.
There is, therefore, a need in the spa and hot tub field for a non-electrical low water level shutoff, preferably one that can be integrated in its operation with an air-actuated pump switch. The present invention is directed to this end.